The present invention relates to filtration of liquids such as water, and especially saline or ocean water. More particularly, the invention relates to cleaning and regeneration of filters used for such filtration as well as an apparatus for carrying out the filtration and for regeneration of the used filters.
Injection of water into an oil-bearing structure is today employed partly to increase and partly to maintain the pressure in an oil-producing well. By injecting water into the oil-bearing layer, a better utilization of the oil field can be achieved. The structure into which the water is pumped usually varies from field to field; however, in general such structures can always be characterized as being microporous.
The pores which will be permeated by the water will have a diameter of approximately 10 .mu.m or less. If the water being forced into the structure contains dispersed particles with a diameter above approximately 10 .mu.m, the structure will then act as a filter, and the structure will become blocked or clogged after a certain period of time.
Thus it is necessary to remove suspended particles above a certain particle size from the water before the water is introduced into the oil-bearing structure. As injection water can, inter alia, be used seawater, or water from lakes, rivers, and the like. Water from such sources will usually contain relatively large amounts of microorganisms, usually algae, having a size in a range 1-100 .mu.m. The total amount of organic material, for instance in water taken from the optimal depths in the North Sea, will be in the range 0.1-0.5 ppm. In order that the microorganisms shall not multiply, the water must further be sterilized, for instance by means of chlorination.
The filtration degree will be dependent on the structure into which the water is to be injected; however, in most cases particles above 10 .mu.m must be removed.
Filtration of water containing marine microorganisms is particularly difficult as such organisms usually form a slime-like and clogging layer on the active surface of the filters, which in a relatively short time results in a complete blocking of the filter.
Conventional re-conditioning methods such as back-washing with water or air is very difficult as relatively high pressures are necessary in order to remove the matter being deposited in and on the very fine-pored material which is utilized for such filtration.
Since back-washing at best is very ineffective and further represents a very high mechanical stress on the filter, the effective life-span of the filter will be relatively short. Consequently, the filter units must be replaced at short intervals, which is very costly both with respect to the costs of the material and in labor.
It is thus an object of the present invention to provide a process for cleaning and regenerating filters used to filter liquids such as water which avoids the noted drawbacks.